Flue gas purification method

ABSTRACT

A method of scrubbing SO x , NO x  compounds and other air toxins from a flue gas stream. In the method, two distinct unit operations are amalgamated to scrub SO x , NO x  and other air toxins compounds from a flue gas stream. More specifically, there is a dry scrubbing operation and a wet scrubbing operation. The dry injection scrubbing operation involves contacting a flue gas stream containing SO x  and NO x  compounds with a sorbent for removing substantially all of the SO x  and NO x  compounds present in the stream. The second wet scrubbing operation involves contacting the stream to remove any residual SO x , NO x  compounds, and other air toxins remaining in the stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is the first application filed for the present invention.

TECHNICAL FIELD

[0002] The present invention relates to a flue gas purification method,and more particularly, the present invention relates to a flue gaspurification method incorporating dry injection and wet scrubbing unitoperations to substantially eliminate SO_(x) and NO_(x) compounds aswell as other air toxic compounds from the flue gas.

BACKGROUND OF THE INVENTION

[0003] In view of new stringent legislation in the United States andelsewhere, greater strides have now had to be made concerning fossilfuels. As is well known, the use of fossil fuels significantlycontributes to air pollution and a multitude of patents have issued withthe objective of mitigating the pollution aspect.

[0004] Globally, the prior art establishes a number of wet chemicalabsorption methods which primarily incorporate wet scrubbers where a hotcontaminated gas is scrubbed or detoxified in a gas liquid contactapparatus with a neutralizing solution. The neutralizing solution cantypically be any suitable aqueous alkaline liquid or slurry to removesulfur oxides and other contaminants present in the flue gas stream. Thegas liquid contacts apparatus are generally employed by power generatingstations and use the wet chemical absorption arrangement incorporatingsodium, calcium, magnesium, etc. to desulfurize flue gas.

[0005] Generally typical of the issued references is U.S. Pat. No.5,082,586, issued Jan. 21, 1992, to Hooper. In the document, a pollutioncontrol reagent compound is provided. The composition includes Nahcoliteand urea for dry injection into a flue gas duct. This results in thereaction of Nahcolite with the SO₂ in the flue gas, while the ureaprecludes the synthesis of NO from NO₂ by the Nahcolite and regulatesthe NO₂ concentration in the exit gas to approximately 50 ppm. Thislimit is essentially the visibility limit.

[0006] In U.S. Pat. No. 5,002,741, issued to Hooper, Mar. 26, 1991, afurther pollution control method is set forth. The process involves highcarbon injection into flue gas together with a sodium based sorbent. Thecomposition removes SO_(x) and NO_(x) compounds. As in the previouslydiscussed reference, there is a specific concern for NO conversion toNO₂. In this case, the discussion indicates that the carbon materialmust have sufficiently high surface area and be mixed with a carriersuch as flyash in order to retard the formation of the NO₂.

[0007] Johnson et al., in U.S. Pat. No. 6,303,083, issued Oct. 16, 2001,disclose a SO_(x) removal process for flue gas treatment. A specificparticle size range for the sorbent is reacted with the flue gas toreduce SO₃ content. The treated flue gas is then reacted in a wetscrubber to reduce SO₂ content.

[0008] A further wet scrubbing system is discussed in U.S. Pat. No.4,263,021, issued Apr. 21, 1981 to Downs et al. The reference teaches acountercurrent gas/liquid contact method between flue gas containingsulfur dioxide and an aqueous slurry solution. The arrangementrecognized in the art as a tray or gas distribution device. The tray hasthe purpose of improving the scrubber performance.

[0009] With respect to the wet precipitators, U.S. Pat. No. 4,441,897,issued Apr. 10, 1984 to Young et al., have been used for many years toremove sulfur trioxide from wet flue streams. In the principal ofoperation, the sulfur trioxide forms an aerosol of sulfuric acid byreaction with water. The aerosol is charged electrically, butsubsequently removed by collection on plates or tubes. This process isalso referred to as wet electrostatic precipitation.

[0010] Further processes which have been incorporated in industry toremove sulfur trioxide include condensation reactions. An example ofsuch a process is referred to as the WSA-SNOX process. This methodinvolves the catalytic conversion of sulfur dioxide to sulfur trioxide.The sulfur trioxide is then removed by condensation in the form ofsulfur acid.

[0011] One problem which has beleaguered the industry is the control ofbrown plume, a consequence of flue gas purification. To this end, U.S.Pat. No. 4,954,324, issued to Hooper, Sep. 4, 1990, provides a processfor baghouse brown plume control where urea or ammonia together withsodium bicarbonate or Nahcolite are injected. This dry injectionprocedure reacts the sodium bicarbonate with SO₂ to form sodium sulphateand removes NO_(x) in the NO form. Urea impedes the conversion of NO toNO₂.

[0012] As is evident from the existing flue gas management protocols, NOand NO_(x) formation present complications in terms of plume control.Consequently, the existence of the plume requires additional unitoperations and still results in the existence of the plume at tolerablelevels.

[0013] The wet scrubbing systems that employ lime, lime stone, soda ashor other alkaline compositions demonstrate efficacy for removal ofsulfur dioxide, but are significantly less efficient at the removal ofsulfur trioxide or sulfuric acid aerosol.

[0014] In terms of electrostatic precipitators, the wet type are usefulto remove particulates and sulfur trioxide (as sulfuric acid and otheraerosols), but such systems fall short on sulfur dioxide removal.Accordingly, there is a requirement for injection of absorbents,reagents or sorbents to control sulfur trioxide and sulfur dioxide, butthe reagent requirement is significant. In an effort to combat theweaknesses of each system, a combination of wet flue gas desulfurizationand wet electrostatic precipitation has been proposed and is effectiveat controlling both sulfur dioxide and sulfur trioxide, however, theelectrostatic precipitator, in view of its design is limited in that thedevice required multiple stages to control sulfur trioxide atconcentrations between 10 and 50 ppm. As is known in the art, thesemultiple stage arrangements are not only expensive and impractical, butthey also pose engineering challenges and require a great deal ofsupport equipment.

[0015] In light of the increasing stringent pollution regulations, thereclearly exists a need for the management of flue gas where both theSO_(x) and NO_(x) compounds can be handled effectively without emissionof brown plume, the need to augment with suppressants or the combinationof equipment which, in the case of the wet flue gas desulfurization andwet electrostatic precipitation, only marginally addresses the problemat a fairly significant expense.

[0016] The methodology set forth herein alleviates all of thelimitations in the prior art techniques.

SUMMARY OF THE INVENTION

[0017] One object of the present invention is to provide an improvedmethod for flue gas purification.

[0018] A further object of one embodiment of the present invention is toprovide a method of scrubbing SO_(x) and NO_(x) compounds from a fluegas stream, comprising:

[0019] a dry injection scrubbing operation and a wet scrubbingoperation, the dry injection scrubbing operation including:

[0020] contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent for removing substantially all of the SO_(x)and a large amount of NO_(x) compounds present in the stream; and thewet scrubbing operation including:

[0021] contacting the stream to remove any residual SO_(x) and NO_(x)compounds remaining in the stream.

[0022] The unification of the dry injection scrubbing operation and awet scrubbing operation advantageously eliminates the concern for brownplume. Previously, reaction of the sodium sorbents resulted in thesynthesis of NO_(x) compounds as plume. The NO_(x) compounds are solublespecies and are easily managed by treatment with the wet scrubbingoperation. In this manner, it is immaterial that NO₂ forms; the plumecannot develop since the NO_(x) (where x=>1 and Y=>2) species areabsorbed in the wet scrubber. Accordingly, the previous requirement forauxiliary suppressant addition is obviated.

[0023] In the combined system set forth herein, the flue gas ispreconditioned by absorbent injection. The absorbent can comprisesuitable reagents or sorbents known to at least diminish theconcentration of the sulfur trioxide. Advantageously, this can beachieved by wet or dry injection with essentially any sorbent orcombinations of sorbent and at any possible location in the system. Drysodium bicarbonate injection has been found to be particularly effectivesince it reacts with the sulfur di- and trioxides as well as the NO_(x)compounds. Generally speaking, the sulfur trioxide is managed to a levelthat is compatable with single stage wet electrostatic precipitatorsinstalled in a wet flue gas desulfurization tower.

[0024] A further object of one embodiment of the presentation is toprovide a method of scrubbing SO_(x) and NO_(x) compounds from a fluegas stream, comprising:

[0025] a dry injection scrubbing operation and a wet scrubbingoperation, the dry injection scrubbing operation including:

[0026] contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent for removing substantially all of the SO_(x)and a large amount of NO_(x) compounds present in the stream;

[0027] the wet scrubbing operation including:

[0028] contacting the stream to remove any residual SO_(x) and NO_(x)compounds remaining in the stream; and

[0029] recirculating unreacted sorbent to the wet scrubbing operation.

[0030] A still further object of one embodiment of the present inventionis to provide a method of scrubbing SO_(x) and NO_(x) compounds from aflue gas stream, comprising:

[0031] a dry injection scrubbing operation and a wet scrubbingoperation, the dry injection scrubbing operation including:

[0032] contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent for removing substantially all of the SO_(x)and a large amount of NO_(x) compounds present in the stream; and

[0033] the wet scrubbing operation including:

[0034] scrubbing the stream from the dry injection scrubbing operationin the presence of an oxidant to remove any residual SO_(x) and NO_(x)compounds remaining in the stream.

[0035] As a particular benefit, the processes set forth herein areuseful to capture air toxics including, as examples, mercury,particulates and a host of heavy metals.

[0036] As set forth herein previously, prior art attempts relating tothe conversion of NO₂ were problematic since a brown plume of NO₂ wasnot captured by downstream equipment. By the combination of thetechnology set forth herein, the wet scrubbing operation efficientlycaptures the NO₂, N₂O₃ and N₂O₅ and other N_(x)O_(y) compounds. Inaddition, at least a portion of the NO is captured by the sodiumbicarbonate.

[0037] Yet another object of one embodiment of the present invention isto provide a method of scrubbing SO_(x) and NO_(x) compounds from a fluegas stream, comprising:

[0038] a wet injection scrubbing operation and a wet scrubbingoperation, the wet injection scrubbing operation including:

[0039] contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent solution for removing substantially all of theSO_(x) and a large amount of NO_(x) compounds present in the stream; and

[0040] the wet scrubbing operation including:

[0041] contacting the stream to remove any residual SO_(x) and NO_(x)compounds remaining in the stream.

[0042] The provision of the oxidant augments the effectiveness of thewet scrubbing and in particular, the oxidation of the NO_(x) compounds.

[0043] With respect to the apparatus, the existing technology has beeneffectively employed and choice for specific components will be readilyapparent to the man skilled in the art.

[0044] Having thus generally described the invention, reference will nowbe made accompanying drawings, illustrating preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIG. 1 is a schematic illustration of a vertical combustorfacility used to generate test data; and

[0046]FIG. 2 is a schematic illustration of the process according to oneembodiment.

[0047] It will be noted that throughout the appended drawings, likefeatures are identified by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXPERIMENTAL

[0048] The apparatus employed to gather the data is illustrated inFIG. 1. The vertical combustor, globally denoted by numeral 10, was theprimary combustor for generating the data.

[0049] Bituminous coal from silo 12 was pulverized in pulverizer 14 andpassed on to silo 16 and subsequently into coal feeder 18. Pre-dried andpulverized coal was conveyed to the combustor via an eductor 20.

[0050] The combustor 10 produced NO_(x) emissions of about 400-500 ppmdvat 2% O₂ excess at the combustor exit and SO_(x) emissions at 2700 to3000 ppm.

[0051] Flue gas compositions (O₂, CO₂, CO, NO and NO₂) were monitoredusing flue gas analyzer 22 located between the combustor 10 and cyclone24.

[0052] For emission control, the combustor 10 was equipped with a hotcyclone, a five-field electrostatic precipitator (ESP) 30 and thecondensing heat exchanger 28 (used as a wet scrubber).

[0053] Dry NaHCO₃ powder was injected against the flue stream in acounter current manner in ports 20 a, 20 b, and 20 c.

[0054] Table 1 sets forward the conditions under which the data wasobtained. TABLE 1 Conditions Common to All Tests Coal Bituminous Heatinput 0.21 MWth (0.7 MBTU/hr) Target O₂ excess in flue gas 2% volume dryTarget NO_(x) concentration 400 ppmdv Flue gas velocity at 150° C. ˜3.4m/s (11 ft/sec) Scrubbing solution flow rate ˜341/min (9 USGPM) NaHCO3injection duration 1 hour, NaHCO₃ in-flight residence 0.5, 1.5 and 3 sectime NaHCO₃ injection temperature 150° C. Conditions Specific to EachTest NaHCO₃ Injection Scrubbing Test ID Rate NaHCO₃ Size Solution _0 6.6kg/hr 45 μm Na₂CO₃ _1 6.6 kg/hr 20 μm Pre-charged _2 5.5 kg/hr 20 μmPre-charged _3 7.7 kg/hr 20 μm Pre-charged Injection Port Port IDResidence time from Port to inlet (sec) 20a 3 20b 1.5 20c 0.5

[0055] Test _(—)0 was a base test to ensure that all components wereoperational. In this test, the NaHCO₃ was first injected in each portfor 5 min. Then, a 1-hour long injection was done in Port 20 a.

[0056] The scrubber pre-charging was done according to the followingspecifications: 1 kg of Na₂CO₃, 29 kg of Na₂SO₄ and 19 kg of Na₂SO₃dissolved in 187 l of water. The pH of the prepared solution was about10.6.

[0057] Table 2 represents the analysis of the coal used. TABLE 2 Coalanalysis Proximate Analysis (wt %) Moisture 1.14 Ash 11.03 Volatiles39.3 Fixed Carbon 48.53 Ultimate Analysis (wt %, dry) Carbon 72.42Hydrogen 4.99 Nitrogen 1.37 Sulphur 3.96 Ash 11.03 Oxygen (diff) 6.10Chlorine (Cl)   790 ppm Fluorine (F)   72 ppm Mercury (Hg) 0.086 ppm

[0058] All combustion trials were conducted at a firing rate of 0.21 MWt(0.7 MBTU/hr) with the O₂ in flue gas being maintained at 2% dv.

[0059] Prior to commencing each suite of combustion trials with aspecific coal, natural gas was burned at 0.3 MWt for at least 8 h with 5vol % O₂ in the flue gas to perform instrumentation checks and to attainthermal equilibrium in the combustor 10 and downstream heat exchanger28.

EXAMPLE 1

[0060] NaHCO₃ was injected at 150° C. for a short period (5 minutes) inall three ports 20 a, 20 b, 20 c at a rate of 6.6 kg/hr to observe itseffects on the concentrations of SO₂ and NO_(x). A 1-hour continuousinjection was then performed in Port 20 a following the shortinjections.

[0061] Sodium carbonate (Na₂CO₃) in water solution was used in scrubber28 as the scrubbing solution and was added during the testing period tomaintain the solution pH at around 7.

[0062] Table 3 summarizes the average flue gas compositions at thecombustor exit and scrubber inlet before any NaHCO₃ injection was made.TABLE 3 Flue gas compositions before injections Combustor Exit Scrubberinlet O₂ (%) 2.08 ± 0.32 5.41 ± 0.22 CO₂ (%) 16.21 ± 0.38  13.65 ± 0.26 CO (ppm)  50 ± 154 100 ± 142 NO_(x) (ppm) 493 ± 54  226 ± 24  SO₂ (ppm)2854 ± 114  2331 ± 58 

[0063] Note that all concentrations are reported on a volumetric and drybasis.

[0064] Injection of sodium bicarbonate started at 0240 pm at Port 20 c(0.5 sec residence time), then proceeded to Ports 20 b and 20 a lastingfor 5 min at each port. Table 4 summarizes the flue gas compositionsduring the injection period. TABLE 4 Flue gas compositions at combustorexit and scrubber inlet during the short period (5 min) sorbentinjections Port 20c Port 20b Port 20a Comb. Scrubber Comb. ScrubberComb. Scrubber Exit inlet Exit inlet Exit inlet O₂ (%) 2.6 ± 0.4 7.2 ±0.5 2.3 ± 0.3 7.1 ± 0.3 2.3 ± 0.2 6.9 ± 0.1 CO₂ (%) 15.6 ± 0.4  11.9 ±0.3  16.3 ± 0.3  12.0 ± 0.2  16.1 ± 0.0  12.4 ± 0.0  CO (ppm) 35 ± 30 67± 78 15 ± 26 28 ± 24 8 ± 3 19 ± 9  NO_(x) (ppm) 491 ± 13  204 ± 11  488± 13  193 ± 13  512 ± 10  162 ± 7  SO₂ (ppm) 2687 ± 96  1637 ± 117  2853± 30  1570 ± 97  2919 ± 57  1344 ± 44 

[0065] Table 5 shows the flue gas compositions during the 1-hourinjection in Port 20 a: TABLE 5 Flue gas compositions at combustor exit,scrubber inlet and outlet during the 1-hour sorbent injections in Port20a Scrubber Scrubber Comb. Exit Inlet Outlet O₂ (%) 2.3 ± 0.2 6.9 ± 0.17.0 ± 0.3 CO₂ (%) 16.1 ± 0.3  12.3 ± 0.2  12.4 ± 0.2  CO (ppm)  30 ± 10736 ± 80 10 ± 1  NO_(x) (ppm) 515 ± 19  152 ± 11  170 ± 7  SO₂ (ppm) 2862± 42  1115 ± 45  15 ± 2 

[0066] A significant reduction in concentration of the SO₂ and NO_(x)was realized immediately upon injection of the NaHCO₃ into the flue gasstream. The effect was enhanced with increasing residence time. Once theNaHCO₃ injection was complete, the concentrations of SO₂ and NO_(x)returned to pre-injection levels.

[0067] A further test was done with NaHCO₃ injection in three ports at aflow rate of 6.6 kg/hr and target injection temperature of 150° C. Theinjection period lasted 1 hour in each port.

[0068] The NaHCO₃ injection started in Port 20 c and proceeded to Ports20 b and 20 a.

[0069] Table 6 summarizes the average flue gas compositions at thecombustor exit and scrubber inlet before any NaHCO₃ injection was made.TABLE 6 Flue gas compositions before injections Combustor Exit Scrubberinlet O₂ (%) 1.87 ± 0.44 4.48 ± 0.49 CO₂ (%) 16.42 ± 0.42  14.11 ± 0.41 CO (ppm)  27 ± 109 46 ± 56 NO_(x) (ppm) 492 ± 47  408 ± 36  SO₂ (ppm)2969 ± 68  2591 ± 157 

[0070] Injection of NaHCO₃ started at 1254 am at Port 20 c (0.5 secresidence time), proceeded to Ports 20 b and 20 a and lasted for 60 minin each port. Table 7 summarizes the flue gas compositions during theinjections. TABLE 7 Flue gas compositions during injections Scrubberinlet before injection Scrubber inlet Scrubber outlet (diluted by duringduring injection air) injection injection Port 20c O₂ (%) 6.10 ± 0.475.68 ± 0.18 5.66 ± 0.12 CO₂ (%) 13.35 ± 0.44  13.41 ± 0.28  13.37 ±0.09  CO (ppm) 45 ± 47  97 ± 142 36 ± 44 NO (ppm) 356 ± 18  215 ± 13 252 ± 13  NO₂ (ppm) 6 ± 2 27 ± 4  4 ± 2 NO_(x) (ppm) 362 ± 21  242 ± 12 256 ± 15  SO₂ (ppm) 2385 ± 64  296 ± 30  11 ± 2  Port 20b O₂ (%) 5.71 ±0.45 5.67 ± 0.14 5.68 ± 0.17 CO₂ (%) 13.46 ± 0.48  13.67 ± 0.00  13.50 ±0.00  CO (ppm) 43 ± 45 43 ± 71 23 ± 23 NO (ppm) 317 ± 24  182 ± 13  202± 13  NO₂ (ppm) 8 ± 2 41 ± 3  6 ± 4 NO_(x) (ppm) 325 ± 24  223 ± 12  208± 13  SO₂ (ppm) 2167 ± 204  245 ± 34  18 ± 4  Port 20a O₂ (%) 5.96 ±0.05 5.74 ± 0.12 5.80 ± 0.19 CO₂ (%) 13.07 ± 0.00  13.54 ± 0.27  13.41 ±0.00  CO (ppm) 13 ± 0  21 ± 32 14 ± 11 NO (ppm) 344 ± 21  113 ± 11  118± 12  NO₂ (ppm) 14 ± 3  76 ± 5  11 ± 5  NO_(x) (ppm) 358 ± 21  189 ± 12 128 ± 14  SO₂ (ppm) 2282 ± 38  160 ± 16  11 ± 3 

[0071] As is evident, a noticeable decrease of NO and SO₂ upon theinjection of NaHCO₃ and the increase of NO₂ was realized. The scrubberwas very effective at removing SO₂ as its concentration droppedprecipitously at the scrubber outlet.

EXAMPLE 2

[0072] This test was done with NaHCO₃ injection in three ports at a flowrate of 5.5 kg/hr and injection temperature of 150° C. The injectionperiod was 1 hour in each port. The scrubber solution was pre-chargedwith: 1 kg of Na₂CO₃, 29 kg of Na₂SO₄ and 19 kg of Na₂SO₃ dissolved in187 l of water. The pH of the prepared solution was about 10.6.

[0073] The NaHCO₃ injection started in Port 20 c and proceeded to Ports20 b and 20 a. After the completion of each injection, the filter of theCEM train downstream of the injection port was immediately changed toensure accurate readings of the flue gas compositions.

[0074] Table 8 summarizes the average flue gas compositions at thecombustor exit and scrubber inlet before any NaHCO₃ injection was made.TABLE 8 Flue gas compositions before injections Combustor Exit Scrubberinlet O₂ (%) 2.07 ± 0.30 4.28 ± 0.34 CO₂ (%) 16.17 ± 0.30  14.52 ± 0.33 CO (ppm) 10 ± 46 21 ± 24 NO_(x) (ppm) 515 ± 57  321 ± 27  SO₂ (ppm) 2937± 86  2438 ± 77 

[0075] Injection of NaHCO₃ started at 1237 am at Port 20 c (0.5 secresidence time), proceeded to Port 20 a lasting for 60 min at each port.Table 9 summarizes the flue gas compositions during the injections.TABLE 9 Flue gas compositions during injections Scrubber inlet beforeinjection Scrubber inlet Scrubber outlet (diluted by during duringinjection air) injection injection Port 20c O₂ (%) 6.18 ± 0.63 6.05 ±0.14 6.21 ± 0.16 CO₂ (%) 13.84 ± 0.44  13.48 ± 0.26  13.41 ± 0.10  CO(ppm)  87 ± 151 17 ± 11 12 ± 12 NO (ppm) 277 ± 33  203 ± 22  211 ± 23 NO₂ (ppm) 0 ± 0 5 ± 3 7 ± 4 NO_(x) (ppm) 277 ± 33  208 ± 21  218 ± 24 SO₂ (ppm) 2208 ± 70  159 ± 21  11 ± 2  Port 20b O₂ (%) 6.18 ± 0.24 6.26± 0.13 6.49 ± 0.14 CO₂ (%) 12.94 ± 0.28  13.23 ± 0.09  13.23 ± 0.22  CO(ppm) 30 ± 65 10 ± 9  6 ± 1 NO (ppm) 280 ± 15  150 ± 23  181 ± 21  NO₂(ppm) 4 ± 2 45 ± 4  1 ± 2 NO_(x) (ppm) 284 ± 16  195 ± 26  183 ± 22  SO₂(ppm) 2364 ± 68  Decreasing to 90 ± 9  150 Port 20a O₂ (%) 6.37 ± 0.176.36 ± 0.11 6.35 ± 0.16 CO₂ (%) 12.88 ± 0.23  12.96 ± 0.20  13.45 ±0.00  CO (ppm) 13 ± 18 10 ± 11 12 ± 18 NO (ppm) 320 ± 35  113 ± 9  125 ±12  NO₂ (ppm) 10 ± 3  58 ± 3  2 ± 3 NO_(x) (ppm) 330 ± 36  171 ± 12  128± 12  SO₂ (ppm) 2303 ± 39  326 ± 24  18 ± 3 

[0076] From a review of the data noted above, there was a noticeabledecrease of NO and SO₂ upon the injection of NaHCO₃ and a significantincrease of NO₂ at scrubber inlet at 1 and 3 sec residence time. Whenthe CEM was moved to scrubber outlet at the end of the third injection,it indicated the immediate increase of the concentrations of NO₂ and SO₂confirming their removal in the scrubber.

EXAMPLE 3

[0077] In the example, NaHCO₃ injection occurred in three ports at aflow rate of 7.7 kg/hr and injection temperature of 150° C. Theinjection period lasted 1 hour in each port. The scrubber solution waspre-charged as 1 kg of Na₂CO₃, 29 kg of Na₂SO₄ and 19 kg of Na₂SO₃dissolved in 187 l of water. The pH of the prepared solution was about10.6.

[0078] The NaHCO₃ injection started in Port 20 c and proceeded to Port20 a.

[0079] Table 10 shows the average injection temperatures for each port.TABLE 10 Average injection temperatures (° C.) Port 20a Port 20b Port20c Up- Down- Up- Down- Up- Down- stream stream stream stream streamstream Injection 155 ± 3 132 ± 5 157 ± 1 133 ± 0 157 ± 5 139 ± 5temperature

[0080] Table 11 summarizes the average flue gas compositions at thecombustor exit and scrubber inlet before any NaHCO₃ injection was made.TABLE 11 Flue gas compositions before injections Combustor Exit Scrubberinlet O₂ (%) 2.14 ± 0.33 4.38 ± 0.19 CO₂ (%) 15.95 ± 0.29  14.23 ± 0.45 CO (ppm) 10 ± 85 28 ± 5  NO_(x) (ppm) 545 ± 114 540 ± 25  SO₂ (ppm) 2964± 127  2672 ± 101 

[0081] Injection of sodium bicarbonate started at 1237 am at Port C (0.5sec residence time), proceeded to Port A lasting for 60 min at eachport.

[0082] Table 12 summarizes the flue gas compositions during theinjections. TABLE 12 Flue gas compositions during injections Scrubberinlet before injection Scrubber inlet Scrubber outlet (diluted by duringduring injection air) injection injection Port 20c O₂ (%) 5.82 ± 0.386.05 ± 0.10 6.11 ± 0.16 CO₂ (%) 12.89 ± 0.38  13.25 ± 0.00  13.02 ±0.17  CO (ppm) 20 ± 1  17 ± 1  14 ± 1  NO (ppm) 480 ± 54  303 ± 28  341± 19  NO₂ (ppm) 7 ± 5 38 ± 4  6 ± 2 NO_(x) (ppm) 486 ± 61  342 ± 34  346± 20  SO₂ (ppm) 2464 ± 57  Decreasing to 12 130 Port 20b O₂ (%) 5.98 ±0.22 5.85 ± 0.11 5.79 ± 0.10 CO₂ (%) 13.05 ± 0.22  13.45 ± 0.16  13.22 ±0.00  CO (ppm) 15 ± 2  17 ± 36 15 ± 15 NO (ppm) 457 ± 7  275 ± 20  286 ±19  NO₂ (ppm) 22 ± 3  58 ± 7  4 ± 1 NO_(x) (ppm) 479 ± 7  333 ± 23  290± 19  SO₂ (ppm) 2303 ± 58  300-400 10 ± 1  Port 20a O₂ (%) 5.67 ± 0.325.86 ± 0.08 5.74 ± 0.12 CO₂ (%) 13.23 ± 0.27  13.36 ± 0.03  13.31 ±0.15  CO (ppm) 25 ± 25 11 ± 3  13 ± 8  NO (ppm) 510 ± 12  224 ± 13  202± 8  NO₂ (ppm) 26 ± 6  88 ± 3  3 ± 2 NO_(x) (ppm) 536 ± 11  312 ± 14 206 ± 7  SO₂ (ppm) 2303 ± 39  218 ± 16  8 ± 1

[0083] There was a decrease of NO and SO₂ upon the injection of NaHCO₃and a pronounced increase of NO₂ at the scrubber inlet at all 3residence times tested. Accordingly, at this injection rate (7.7 kg/hr),the accumulation of NaHCO₃ powder on the CEM filter was quite rapid.During the third injection at Port 20 a, the CEM was first located atthe scrubber outlet and moved to the scrubber inlet at the end of theinjection in order to obtain a more reliable SO₂ reading.

[0084] The last 3 tests all showed that, upon injection of NaHCO₃ in theflue stream, concentrations of SO₂ and NO decreased immediately, whileNO₂ concentration increased. Once the injection was stopped, theconcentrations of SO₂ and NO rapidly returned to the pre-injectionlevels. The NaHCO₃ injection did not have any effect on theconcentrations of the other monitored species (O₂, CO₂ and CO).

[0085] For all three tests, the scrubber solution was pre-chargedaccording to 1 kg of Na₂CO₃, 29 kg of Na₂SO₄ and 19 kg of Na₂SO₃dissolved in 187 l of water. The pH of the prepared solution was about10.6. When the scrubbing started, the pH value decreased slowly assulfur was dissolved in the solution. However, when the NaHCO₃ injectionstarted, the pH value of the scrubbing solution stayed steady at about7.5.

[0086] From Table 13, it can be seen that the scrubber was veryeffective in removing NO₂ produced in the flue stream after theinjection of NaHCO₃. The scrubber was also very effective at removingSO₂.

[0087] Having described the test facility and the data collected, inconnection with establishing the effectiveness of the injection andscrubbing operations, reference will now be made to FIG. 2 whichschematically illustrates one embodiment of a plant design. The overallplant design is referenced by numeral 40 with the combustion systemfrom, for example, a power station being referenced by numeral 42. Thecombustion products are first treated in an electrostatic precipitatoror baghouse 44 and subsequently discharged through a flue gas duct 46.In an attempt to further increase the efficiency of the overall system,oxidant material may be injected into the flue gas duct at any number oflocations such as at or approximate the inlet 48 or approximate theoutlet 50. At this oxidation step, is useful to convert uncaptured NOand NO₂ to be converted to NO₂, N₂O₃, N₂O₅ and N_(x)O_(y) inter alia.The oxidation steps 48 and 50 are augmented by the injection step withsodium bicarbonate, the injection being broadly denoted by numeral 52.Although the sodium bicarbonate injection step is preferentially a dryinjection step, it will be clearly understood by those skilled in theart that the injection step can also be wet with essentially any alkalicompound and at any of several locations from the flue gas duct to thewet scrubber to be discussed hereinafter.

[0088] Suitable oxidants will be appreciated by those skilled, however,examples include hydrogen peroxide, ozone, sodium chlorate or compounds(NaClO_(x) where x is 1 through 4) or any combination of thesematerials. Once having been treated with a dry injection step, the fluegas stream now partially devoid of NO_(x) compounds is treated in a wetto dry transition device 54 and then subsequently on to the wetscrubbing operation in wet scrubber 56. Any suitable scrubber 56 may beincorporated and will be essentially the choice of the designer based onthe requirements of the overall circuit. Typical manufactures of wetscrubbers include The Babcock and Wilcox Company, Marsulex, KawaskiHeavy Industries, Mitsui, Chiyoda, Thyssen KEA, inter alia. Numerals 58and 60 denote further possible oxidant injection points where theaqueous solution of the oxidant is recirculated into the scrubber 56. Asuitable pump 62 may be included with each circulation loop of theoxidant. These steps are optional, since it has been indicated hereinpreviously that the oxidant can be introduced at any point from the fluegas duct to the wet scrubber and still function to achieve the goal ofoxidizing any compounds present. The solution from scrubber 56, broadlydenoted by numeral 64 may be removed from time to time for processing.

[0089] As a further optional step, a wet electrostatic precipitator maybe introduced into the circuit, the former being represented by numeral66 where the gas stream is passed through the electrostatic precipitatorto polish the flue gas of any further particulate, fine particulates,water droplets or aerosols from the stream. This is an optional step andis not essential to the process. Once through the ESP 66, the flue gascan then be discharged through the stack 68. The wet esp 66 may or maynot be an extension to the wet scrubber 56. An alternative, shown indashed lines is illustrated in FIG. 2.

[0090] In terms of the overall reactions that occur in the process, thereactions that occur in the dry injection phase are simply those thatinvolve the sodium bicarbonate contacting the SO_(x) and NO_(x)compounds. Exemplary of the actions of the SO_(x) chemistry that occurin the injection apparatus include the following:

[0091] 1) NaHCO₃

Na₂CO₃+CO₂(g)+H₂O(g)

[0092] 2) 2*NaHCO₃+SO₂(g)

Na₂SO₃+2*CO₂(g)+H₂O(g)

[0093] 3) 2*NaHCO₃+SO₃(g)

Na₂SO₄+2*CO₂(g)+H₂O(g)

[0094] 4) Na₂CO₃+SO₂(g)

Na₂SO₃+CO₂(g)

[0095] 5) Na₂CO₃+SO₃(g)

Na₂SO₄+CO₂(g)

[0096] 6) 2*NaNO₃+SO₂(g)

Na₂SO₄+2*NO₂(g)

[0097] 7) 2*NaNO₂+SO₂(g)

Na₂SO₄+2*NO(g)

[0098] 8) 2*NaNO₂+SO₂(g)+O₂(g)

Na₂SO₄+2*NO₂(g)

[0099] 9) SO₂(g)+H₂O

HSO₃+H

[0100] In addition to the SO_(x) reactions there are additionally NO_(x)reactions occurring in the injection phase which include the following:

[0101] 1) Na₂SO₃+2*NO₂(g)+O₂(g)

2*NaNO₃+SO₃(g)

[0102] 2) Na₂SO₃+2*NO(g)+2*O₂(g)

2*NaNO₃+SO₃(g)

[0103] 3) Na₂SO₃+2*NO(g)+O₂(g)

2*NaNO₂+SO₃(g)

[0104] 4) Na₂CO₃+2*NO₂(g)+O₂(g)

2*NaNO₃+NO(g)+CO₂(g)

[0105] 5) 2*NO(g)+O₂(g)

2*NO₂(g)

[0106] 6) NO(g)+NO₂(g)

N₂O₃(g)

[0107]

[0108] 7) 2*NO₂(g)

N₂O₄(g)

[0109] 8) N₂O₃(g)+H₂O

2*HNO₂

[0110] 9) N₂O₃(g)+2*NaOH

2*NaNO₂+H₂O

[0111] 10) 2*NO₂(g)+H₂O

HNO₂+HNO₃

[0112] 11) 2*NO₂(g)+2*NaOH

NaNO₂+NaNO₃+H₂O

[0113] 12) 3*NO₂(g)+H₂O

NO(g)+2*HNO₃

[0114] 13) 3*NO₂(g)

N₂O₅(g)+NO(g)

[0115] 14) NaNO₂+NO₂(g)

NO(g)+NaNO₃

[0116] 15) N₂O₄(g)+H₂O

HNO₂+HNO₃

[0117] 16) 3*HNO₂

2*NO(g)+H₂O+HNO₃

[0118] 17) N₂O₅(g)+H₂O

2*HNO₃

[0119] 18) HNO₃+NaOH

NaNO₃+H₂O

[0120] In terms of the reactions that occur in the wet scrubber, many ofthe NO_(x) reactions indicated above occur in the wet scrubbing phase aswell as the following acid gas reactions:

[0121] 1) 2*HCl+Na₂CO₃

2*NaCl+CO₂+H₂O

[0122] 2) 2*HF+Na₂CO₃

2*NaF+CO₂+H₂O

[0123] 3) H₂S+2*O₂

H₂SO₄

OH+HSO₃

[0124] 4) Na₂S+2*O₂

2*Na₂SO₄

[0125] 5) 8*NO(g)+Na₂S

NaSO₃(NO)₂+3*N₂O

[0126] 6) NaSO₃(NO)₂+3*N₂O

NaSO₄+4*N₂O

[0127] 7) H₂SO₄+Na₂CO₃

Na₂SO₄+CO₂+H₂O

[0128] As discussed herein previously, the oxidant loops where oxidantis injected into the wet scrubber by points 58 and 60. Typical of thereactions that will occur from an oxidation point of view include thefollowing:

[0129] 1) O(g)+O₂(g)

O₃(g)

[0130] 2) NO(g)+O₃(g)

NO₂(g)+O₂(g)

[0131] 3) 2*NO(g)+O₃(g)

N₂O₅(g)

[0132] 4) 2*NO(g)+O₂(g)

2*NO₂(g)

[0133] 5) 2*NO₂(g)+O₃(g)+H₂O

2*HNO₃(g)+O₂(g)

[0134] 6) NO(g)+NaClO

NaCl+NO₂(g)

[0135] 7) H₂S+4*NaClO

4*NaCl+H₂SO₄

[0136] 8) H₂S+H₂O₂

S+2*H₂O

[0137] 9) 4*NO(g)+3*NaClO₂+4*NaOH

4*NaNO₃+3*NaCl+2*H₂O

[0138] 10) 4*NO₂(g)+NaClO₂+4*NaOH

4*NaNO₃+NaCl+2*H₂O

[0139] 11) 2*Na₂SO₃+NaClO₂

2*Na₂SO₄+NaCl

[0140] 12) 3*H₂O₂+2*NO(g)

HNO₃+2*H₂O

[0141] 13) H₂O₂+HNO2

HNO₃+H₂O

[0142] As a particular convenience, the dry injection scrubbingoperation as well as the wet scrubbing operation are particularly usefulin reducing other air toxic compounds present in the flue gas.

[0143] Based on the Environmental Protection Agency in the UnitedStates, the listed air toxic compounds include the following:

[0144] Acetaldehyde

[0145] Acetamide

[0146] Acetonitrile

[0147]

[0148] Acetophenone

[0149] 2-Acetylaminofluorene

[0150] Acrolein

[0151] Acrylamide

[0152] Acrylic acid

[0153] Acrylonitrile

[0154] Allyl chloride

[0155] 4-Aminobiphenyl

[0156] Aniline

[0157] o-Anisidine

[0158] Asbestos

[0159] Benzene (including benzene from gasoline)

[0160] Benzidine

[0161] Benzotrichloride

[0162] Benzyl chloride

[0163] Biphenyl

[0164] Bis(2-ethylhexyl)phthalate (DEHP)

[0165] Bis(chloromethyl) ether

[0166] Bromoform

[0167] 1,3-Butadiene

[0168] Calcium cyanamide

[0169] Captan

[0170] Carbaryl

[0171] Carbon disulfide

[0172] Carbon tetrachloride

[0173] Carbonyl sulfide

[0174]

[0175] Catechol

[0176] Chloramben

[0177] Chiordane

[0178] Chlorine

[0179] Chloroacetic acid

[0180] 2-Chloroacetophenone

[0181] Chlorobenzene

[0182] Chlorobenzilate

[0183] Chloroform

[0184] Chloromethyl methyl ether

[0185] Chloroprene

[0186] Cresol/Cresylic acid (mixed isomers)

[0187] o-Cresol

[0188] m-Cresol

[0189] p-Cresol

[0190] Cumene

[0191] 2,4-D, salts and esters (2,4-Dichlorophenoxyacetic

[0192] Acid)

[0193] DDE (1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene)

[0194] Diazomethane

[0195] Dibenzofuran

[0196] 1,2-Dibromo-3-chloropropane

[0197] Dibutyl phthalate

[0198] 1,4-Dichlorobenzene

[0199] 3,3′-Dichlorobenzidine

[0200] Dichloroethyl ether (Bis[2-chloroethyl]ether)

[0201]

[0202] 1,3-Dichloropropene

[0203] Dichlorvos

[0204] Diethanolamine

[0205] Diethyl sulfate

[0206] 3,3′-Dimethoxybenzidine

[0207] 4-Dimethylaminoazobenzene

[0208] N,N-Dimethylaniline

[0209] 3,3′-Dimethylbenzidine

[0210] Dimethylcarbamoyl chloride

[0211] N,N-Dimethylformamide

[0212] 1,1-Dimethylhydrazine

[0213] Dimethyl phthalate

[0214] Dimethyl sulfate

[0215] 4,6-Dinitro-o-cresol (including salts)

[0216] 2,4-Dinitrophenol

[0217] 2,4-Dinitrotoluene

[0218] 1,4-Dioxane (1,4-Diethyleneoxide)

[0219] 1,2-Diphenylhydrazine

[0220] Epichlorohydrin (1-Chloro-2,3-epoxypropane)

[0221] 1,2-Epoxybutane

[0222] Ethyl acrylate

[0223] Ethylbenzene

[0224] Ethyl carbamate (Urethane)

[0225] Ethyl chloride (Chloroethane)

[0226] Ethylene dibromide (Dibromoethane)

[0227] Ethylene dichloride(1,2-Dichloroethane)

[0228]

[0229] Ethylene glycol

[0230] Ethyleneimine (Aziridine)

[0231] Ethylene oxide

[0232] Ethylene thiourea

[0233] Ethylidene dichloride (1,1-Dichloroethane)

[0234] Formaldehyde

[0235] Heptachlor

[0236] Hexachlorobenzene

[0237] Hexachlorobutadiene

[0238] 1,2,3,4,5,6-Hexachlorocyclohexane (all stereo isomers, includinglindane)

[0239] Hexachlorocyclopentadiene

[0240] Hexachloroethane

[0241] Hexamethylene diisocyanate

[0242] Hexamethylphosphoramide

[0243] Hexane

[0244] Hydrazine

[0245] Hydrochloric acid (Hydrogen Chloride)

[0246] Hydrogen fluoride (Hydrofluoric acid)

[0247] Hydroquinone

[0248] Isophorone

[0249] Maleic anhydride

[0250] Methanol

[0251] Methoxychlor

[0252] Methyl bromide (Bromomethane)

[0253] Methyl chloride (Chloromethane)

[0254]

[0255] Methyl chloroform (1,1,1-Trichloroethane)

[0256] Methyl ethyl ketone (2-Butanone)

[0257] Methylhydrazine

[0258] Methyl iodide (Iodomethane)

[0259] Methyl isobutyl ketone (Hexone)

[0260] Methyl isocyanate

[0261] Methyl methacrylate

[0262] Methyl tert-butyl ether

[0263] 4,4′-Methylenebis(2-chloroaniline)

[0264] Methylene chloride (Dichloromethane)

[0265] 4,4′-Methylenediphenyl diisocyanate (MDI)

[0266] 4,4′-Methylenedianiline

[0267] Naphthalene

[0268] Nitrobenzene

[0269] 4-Nitrobiphenyl

[0270] 4-Nitrophenol

[0271] 2-Nitropropane

[0272] N-Nitroso-N-methylurea

[0273] N-Nitrosodimethylamine

[0274] N-Nitrosomorpholine

[0275] Parathion

[0276] Pentachloronitrobenzene (Quintobenzene)

[0277] Pentahlorophenol

[0278] Phenol

[0279] p-Phenylenediamine

[0280] Phosgene

[0281]

[0282] Phosphine

[0283] Phosphorus

[0284] Phthalic anhydride

[0285] Polychlorinated biphenyls (Aroclors)

[0286] 1,3-Propane sultone

[0287] beta-Propiolactone

[0288] Propionaldehyde

[0289] Propoxur (Baygon)

[0290] Propylene dichloride (1,2-Dichloropropane)

[0291] Propylene oxide

[0292] 1,2-Propylenimine (2-Methylaziridine)

[0293] Quinoline

[0294] Quinone (p-Benzoquinone)

[0295] Styrene

[0296] Styrene oxide

[0297] 2,3,7,8-Tetrachlorodibenzo-p-dioxin

[0298] 1,1,2,2-Tetrachloroethane

[0299] Tetrachloroethylene (Perchloroethylene)

[0300] Titanium tetrachloride

[0301] Toluene

[0302] Toluene-2,4-diamine

[0303] 2,4-Toluene diisocyanate

[0304] o-Toluidine

[0305] Toxaphene (chlorinated camphene)

[0306] 1,2,4-Trichlorobenzene

[0307] 1,1,2-Trichloroethane

[0308]

[0309] Trichloroethylene

[0310] 2,4,5-Trichlorophenol

[0311] 2,4,6-Trichlorophenol

[0312] Triethylamine

[0313] Trifluralin

[0314] 2,2,4-Trimethylpentane

[0315] Vinyl acetate

[0316] Vinyl bromide

[0317] Vinyl chloride

[0318] Vinylidene chloride (1,1-Dichloroethylene)

[0319] Xylenes (mixed isomers)

[0320] o-Xylene

[0321] m-Xylene

[0322] p-Xylene

[0323] Antimony Compounds

[0324] Arsenic Compounds (inorganic including arsine)

[0325] Beryllium Compounds

[0326] Cadmium Compounds

[0327] Chromium Compounds

[0328] Cobalt Compounds

[0329] Coke Oven Emissions

[0330] Cyanide Compounds

[0331] Glycol ethers

[0332] Lead Compounds

[0333] Manganese Compounds

[0334] Mercury Compounds

[0335]

[0336] Fine mineral fibers

[0337] Nickel Compounds

[0338] Polycyclic Organic Matter

[0339] Radionuclides (including radon)

[0340] Selenium Compounds

[0341] In conclusion, by combining dry injection and wet scrubbingoperations, the concentrations of SO₂ and NO_(x) were reducedimmediately primarily due to their respective chemical reactions withNaHCO₃. Other sorbents clearly will also provide effectiveness includingthe calcium and magnesium based sorbents such as calcium carbonate,calcium bicarbonate, calcium hydroxide, magnesium carbonate, magnesiumbicarbonate, magnesium hydroxide or any combination of these.

[0342] Reference to U.S. Pat. Nos. 6,143,263 and 6,303,083 may be madefor other examples in SO_(x) removal.

[0343] The scrubber proved very effective at removing NO₂ which canaccount for a significant portion of the overall NO_(x); the scrubberwas also effective in removing sulfuric compounds resulting in near zeroSO₂ emission.

[0344] Although embodiments of the invention have been described above,it is not limited thereto and it will be apparent to those skilled inthe art that numerous modifications form part of the present inventioninsofar as they do not depart from the spirit, nature and scope of theclaimed and described invention.

We claim:
 1. A method of scrubbing SO_(x) and NO_(x) compounds from aflue gas stream, comprising: a dry injection scrubbing operation and awet scrubbing operation, said dry injection scrubbing operationincluding: contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent for removing substantially all of the SO_(x)and a large amount of NO_(x) compounds present in said stream; and saidwet scrubbing operation including: contacting said stream to remove anyresidual SO_(x) and NO_(x) compounds remaining in said stream.
 2. Themethod as set forth in claim 1, wherein said sorbent is a sodium basedsorbent selected from the group consisting of sodium bicarbonate, sodiumcarbonate, sodium hydroxide, or combinations thereof.
 3. The method asset forth in claim 1, wherein said sorbent is a calcium based sorbentselected from the group consisting of calcium carbonate, calciumbicarbonate, calcium hydroxide and combinations thereof.
 4. The methodas set forth in claim 1, wherein said sorbent is a magnesium basedsorbent selected from the group consisting of magnesium carbonate,magnesium bicarbonate, magnesium hydroxide and combinations thereof. 5.The method as set forth in claim 1, wherein said sorbent comprises acombination of sodium, magnesium and calcium sorbents.
 6. The method asset forth in claim 1, wherein said dry injection scrubbing operationproduces sodium sulfate, sodium sulfite, sodium fluoride, sodiumchloride, sodium nitrite, sodium carbonate and/or sodium nitrate.
 7. Themethod as set forth in claim 1, wherein said SO_(x) and NO_(x) compoundsinclude SO₂, SO₃, NO₂, N₂O₃, N₂O₅, N_(x)O_(y) and dimers thereof.
 8. Themethod as set forth in claim 1, further including the step ofrecirculating unreacted sorbent for use in said wet scrubbing operation.9. The method as set forth in claim 1, wherein said method furtherincludes the step of oxidizing said flue gas stream.
 10. The method asset forth in claim 9, wherein said method further includes the step ofoxidizing said stream subsequent to treatment in either or both of saidwet scrubbing operation and said dry scrubbing operation.
 11. The methodas set forth in claim 1, wherein said step of oxidizing includes the useof an oxidant selected from the group consisting of hydrogen peroxide,ozone, NaClO_(x), where x is 1 through 4, or a combination thereof. 12.The method as set forth in claim 1, further including the step ofreducing air toxic compounds present in said flue gas by reaction withsaid dry injection scrubbing operation and said wet scrubbing operationand oxidant addition.
 13. A method of scrubbing SO_(x) and NO_(x)compounds from a flue gas stream, comprising: a dry injection scrubbingoperation and a wet scrubbing operation, said dry injection scrubbingoperation including: contacting a flue gas stream containing SO_(x) andNO_(x) compounds with a sorbent for removing substantially all of theSO_(x) and a large amount of NO_(x) compounds present in said stream;said wet scrubbing operation including: contacting said stream to removeany residual SO_(x) and NO_(x) compounds remaining in said stream; andrecirculating unreacted sorbent to said wet scrubbing operation.
 14. Themethod as set forth in claim 13, further including the step of oxidizingsaid stream.
 15. The method as set forth in claim 13, wherein saidsodium based sorbents are selected from the group consisting of sodiumbased sorbents, calcium based sorbents, magnesium based sorbents andcombinations thereof.
 16. A method of scrubbing SO_(x) and NO_(x)compounds from a flue gas stream, comprising: a dry injection scrubbingoperation and a wet scrubbing operation, said dry injection scrubbingoperation including: contacting a flue gas stream containing SO_(x) andNO_(x) compounds with a sorbent for removing substantially all of theSO_(x) and a large amount of NO_(x) compounds present in said stream;and said wet scrubbing operation including: scrubbing said stream fromsaid dry injection scrubbing operation in the presence of an oxidant toremove any residual SO_(x) and NO_(x) compounds remaining in saidstream.
 17. The method as set forth in claim 16, further including thestep of recirculating unreacted sorbent to said wet injection scrubbingoperation.
 18. The method as set forth in claim 16, wherein said oxidantis selected from the group consisting of hydrogen peroxide, ozone,NaClO_(x), where x is 1 through 4, or a combination thereof.
 19. Themethod as set forth in claim 16, wherein said stream from said dryinjection scrubbing operation is exposed to oxidant.
 20. The method asset forth in claim 16, wherein said stream from said dry injectionscrubbing process produces sodium sulfate, sodium sulfite, sodiumfluoride, sodium chloride, sodium nitrite, sodium carbonate and/orsodium nitrate.
 21. A method of scrubbing SO_(x) and NO_(x) compoundsfrom a flue gas stream, comprising: a wet injection scrubbing operationand a wet scrubbing operation, said wet injection scrubbing operationincluding: contacting a flue gas stream containing SO_(x) and NO_(x)compounds with a sorbent solution for removing substantially all of theSO_(x) and a large amount of NO_(x) compounds present in said stream;and said wet scrubbing operation including: contacting said stream toremove any residual SO_(x) and NO_(x) compounds remaining in saidstream.
 22. The method as set forth in claim 21, wherein said streamfrom said wet scrubbing operation is polished in a wet electrostaticprecipitator.
 23. the method as set forth in claim 16, wherein saidstream from said wet scrubbing operation is polished in a wetelectrostatic precipitator.
 24. The method as set forth in claim 13,wherein said stream from said wet scrubbing operation is polished in awet electrostatic precipitator.
 25. The method as set forth in claim 22,further including removing other air toxins and fine particulate matterin said electrostatic precipitator.